In a communication system, multicast and broadcast are techniques for transferring data from one source to multiple destinations. For instance, in the Ethernet, the Internet Group Management Protocol (IGMP) is a technique in Internet Protocol (IP) used for multicast.
Along with the development of mobile communications, multicast and broadcast find increasing applications in mobile networks. For instance, in a conventional mobile network, the Cell Broadcast Service (CBS) allows low bit-rate data to be transferred to all users via a shared broadcasting channel of a cell. This service is categorized as a service of message.
At present, development of mobile communications has made users' demand for mobile communications go beyond phone communications and message services. Along with the rapid development of the Internet, there is emerging a great deal of multimedia services, some applications of which require that multiple users be able to receive the same data at the same time, e.g. video on demand, telecast, video conference, network-based education, and interactive video games. Compared with conventional data, these mobile and multimedia services feature large data flow, long time duration, and high sensitivity to time delay. The existing techniques of IP multicast make it possible to implement these mobile and multimedia services in the form of multicast or broadcast on cabled IP networks. However, as mobile networks have special network architectures, entities of function and wireless interfaces, which are all different from those of a cabled IP network, existing IP multicast techniques are not applicable to mobile networks.
In order to solve the problems mentioned above and make an efficient use of resources of mobile networks, the WCDMA/GSM global standardization organization, 3GPP, has put forward the solution to Multimedia Broadcast/Multicast Service (MBMS), designed to provide services of transferring data from one source to multiple users in mobile networks so as to share network resources and improve the utility rate thereof, especially the utility rate of resources of wireless interface. MBMS defined by 3GPP can implement not only low-rate text multicast and broadcast of messages, but also multicast and broadcast of high-rate multimedia traffic, which is no doubt the trend of future development of mobile data transmission.
The system architecture of MBMS defined by 3GPP is as shown in FIG. 1, where the Broadcast Multicast-Service Center (BM-SC) is a newly-added mobile network functional entity to support MBMS traffic, which is the entrance of content providers (i.e. sources of multicast/broadcast) used in authorization and in initiating an MBMS bearer as well as transferring MBMS contents according to pre-defined schedules. In addition, functional entities, such as user equipment (UE), UMTS Terrestrial Radio Access Network (UTRAN), GSM EDGE Radio Access Network (GERAN), Serving GPRS Support Node (SGSN), and GPRS Gateway Support Node (GGSN), are enhanced to incorporate relevant functions of MBMS.
MBMS is implemented in two modes, the multicast mode and the broadcast mode. As there are differences between the multicast mode and the broadcast mode in service demand, the service procedures thereof are different.
The flowchart of MBMS multicast mode is as shown in FIG. 2, including such procedures as Subscription, Service announcement, Subscriber Joining, Session Start, MBMS notification, Data transfer, Session Stop, and Subscriber Leaving.
In the MBMS multicast mode, a user joins in the MBMS multicast service by an MBMS activation procedure such that the network could know which users desire to receive a certain specific MBMS service. The network nodes create, through an MBMS registration procedure, a distributing tree from BM-SC to Base Station Controller (BSC)/Radio Network Controller (RNC) via GGSN and SGSN so as to allow the transfer of the session attributes and data of MBMS. The registration procedure creates the MBMS context bearer at relevant nodes. When BM-SC is ready for transferring data, an MBMS Session Start procedure will be triggered. The Session Start procedure activates all the bearer resources on the network needed for transferring MBMS data, and notifies the interested UE that the data transfer is about to start. By this procedure, BM-SC provides the relevant network nodes with the session attributes, such as Quality of Service (QoS), MBMS service domain, and parameter of estimated session duration. This procedure will also trigger such jobs as session notification on the access network by RNC, counting of cell users, selection of radio bearer type, set-up of wireless and cabled bearer plains. BM-SC will start transferring multicast data after the down-stream nodes complete the appropriate jobs. Each node transfers the multicast data through the bearer created in the Session Start procedure, until UE.
The flowchart of MBMS broadcast mode is as shown in FIG. 3, including such procedures as Service announcement, Session Start, MBMS notification, Data transfer, and Session Stop.
In the MBMS broadcast mode, as information of a broadcast service is sent to all users in the radio network, the MBMS registration procedure is not needed at each network node. When BM-SC is ready for transferring data, an MBMS Session Start procedure will be triggered. The Session Start procedure activates all the bearer resources in the network needed for transferring MBMS data. By this procedure, BM-SC provides the relevant interested network nodes with the session attributes, such as the Terminal Mobile Group Identity (TMGI) of the MBMS bearer traffic, Quality of Service (QoS), MBMS service domain, and parameter of estimated session duration (if there exists). This procedure will also trigger such jobs as set-up of wireless and cabled bearer plains. BM-SC will start transferring broadcast data after the down-stream nodes complete the appropriate jobs. Each node transfers the broadcast data through the bearer created in the Session Start procedure, until UE.
It can be seen by persons skilled in the art that the main service procedures of MBMS broadcast mode and multicast mode are similar, both including the processing in the successive procedures of Service announcement, Session Start, MBMS notification, Data transfer, and Session Stop. The difference of the two modes lies in that the multicast mode also includes UE subscribing to the appropriate multicast group, activating the service, and generating appropriate charging information based on the time when the UE joins and leaves.
There are two modes in which MBMS service is provided at wireless interfaces: one is the Point to Point (PTP) mode, the other is the Point to Multipoint (PTM) mode. As power control can be made in the PTP mode, this mode is preferably used when there are fewer users. If the number of users increases, however, the PTP mode will consume a lot of radio resources and inevitably lead to a higher transmitting power of the base station. If the PTM mode is used when there are more users, on the other hand, not only the resources of wireless interface will be saved, but also the transmitting power of the base station will be saved. In order to enable RNC to determine a bearer mode according to the number of users in each cell who demand a certain MBMS service, the MBMS system introduces the counting and recounting procedures.
The counting procedure refers to the procedure by which RNC counts the number of users within a cell receiving an MBMS service when the session of this MBMS service starts while the recounting procedure is to recount the number of users during the session so as to determine that the PTM mode adopted is still the currently suitable bearer mode. In the counting procedure, it is mainly the users in the idle state that are counted. After receiving the counting instruction, users in the idle state need to set up a radio resource control (RRC) connection, then UTRAN will initiate a procedure of setting up Packet Mobility Management (PMM) connection. Thereafter, CN will obtain the list of services this user joins through a UE Linking procedure. This is in fact the procedure of a Packet Switching (PS) connection set up between the user and CN, and RNC obtains from the PS domain of CN the services this user joins via the interface Iu-PS. In this description, Iu refers to the standard interface between RNC and CN.
If a user has not set up a PS connection with the network, in another word, there is no Iu-PS interface between the network and the user, then the relevant information of the services the user joins may be obtained as well by UTRAN when needed via the established Iu-CS interface. In this description, CS is the short form for circuit switching.
When adopting the PTP bearer mode, RNC needs to identify a service using the Network Service Access Point Identifier (NSAPI) corresponding to the service the user joins. At the user side, NSAPI is used in indicating the Packet Data Protocol (PDP)-Service Access Point (SAP), i.e. PDP-SAP, while in SGSN and GGSN, NSAPI is used in indicating the PDP context associated with the PDP address. When requesting for activation of a PDP context, UE needs to select a NSAPI not used by itself.
FIG. 4 is a schematic diagram illustrating the use of NSAPI. As shown in FIG. 4, UE receives IP packets from the SAP with an IP address A (i.e. the IP address, A SAP), makes Protocol Data Units (PDU) into packets, and initializes the NSAPI of this SAP as NSAPI-1. After receiving the IP PDU, SGSN analyzes NSAPI-1, and decides to send the data of IP PDU to the GGSN associated with the IP address A. NSAPI has a corresponding relationship with the International Mobile Subscriber Identity (IMSI). It can be seen from the above example that the role of NSAPI is primarily for identifying the route on the network layer through the IMSI of the user.
This invention relates to the procedure of “Session Start” in an MBMS service. When UTRAN needs to obtain from the network the services a user joins, it also needs to obtain from the network the NSAPI of the user in connection with each service used in identifying the routing of the service the user joins, i.e. used in indicating the service information.
Obviously, for a user, the service identity may as well include the information of Radio Access Bearer Identity (RAB ID) or information of Transaction Identity (TI).
In the prior art, there are two ways in which UTRAN obtains from CN the list of services a user joins, one is the way without PS connection, the other is the way with PS connection.
FIG. 5 is the flowchart for UTRAN obtaining from CN the list of services a user joins when there is no PS connection. When there is no PS connection, a user has only the Iu-CS interface but no Iu-PS interface, i.e. this user is in the connection with RRC and at the PMM-IDLE state. In this case, the process in which UTRAN obtains from CN the list of services the user joins includes primarily the steps of:
Step 501: UE sets up a CS connection with the MSC of CN, i.e. sets up an Iu connection in the CS domain, realizing the signaling connection from UE to MSC; at this time, the Iu of UE in the PS domain is in the PMM-IDLE state, i.e. there is no signaling connection at the Iu-PS interface.
Step 502: RNC requests, in the non-connection mode, SGSN for the list of services this user joins, and the requesting message sent is MBMS SERVICE ID REQ, where the IMSI of the UE is contained.
Step 503: SGSN responds with the message MBMS SERVICE ID RESPONSE, where all the lists of services the user joins are included.
FIG. 6 is the flowchart for UTRAN obtaining from CN the list of services a user joins with a PS connection. When there is a PS connection, i.e. there is a signaling connection at the Iu-PS interface, RAN will send message using the existing procedure of UE Linking, then the process in which UTRAN obtains from CN the list of services the user joins includes primarily the steps of:
Step 601: RNC initiates to CN a procedure of setting up PMM connection.
Step 602: CN informs RNC of the list of services the user joins through a special Iu procedure, i.e. through the signaling of MBMS UE LINKING REQUEST.
Step 603: RNC returns to CN the signaling of MBMS UE LINKING RESPONSE, informing CN that the list of services the user joined has been obtained.